[Internal] Improve Lock Error handling

[stevensJourney]

Overview

It's currently tricky to throw Errors from Swift closure functions which are provided to the Kotlin SDK.

We currently achieve exception propagation for the readLock, readTransaction, writeLock and writeTransaction methods by implementing TransactionCallback and LockCallback wrappers on the Swift side. These wrappers:

• Run the provided Swift closure and catch any thrown exceptions
• Return the exception as the result of the wrapped closure as a PowerSyncException instance
• The Kotlin SDK then detects this exception and throws the exception on the Kotlin side

SKIEE has known limitations with generics. Which causes some rather strange requirements for the TransactionCallback and LockCallback implementations.

The execute method of these implementations should be able to return Any? (a nullable response). But this is not possible due to Objective C limitations:

Throwing method cannot be an implementation of an '@objc' requirement because it returns a value of optional type 'Any?'; 'nil' indicates failure to Objective-CSourceKit

This causes us to define the execute method as returning Any which works, but prints a warning on every compile.

func execute(transaction: PowerSyncKotlin.PowerSyncTransaction) throws -> Any {
          - warning: result of 'execute(transaction:)' has different optionality than expected by protocol 'ThrowableTransactionCallback'
52          do {
53              return try callback(

Furthermore. When enabling the Swift 6 toolchain while making Swift 6 declaration changes. The compiler seems to crash when processing the TransactionCallback.swift file.

This PR removes the need for TransactionCallback and LockCallback in the Swift SDK, by making use of the changes in Kotlin PR

[Copilot]

Pull Request Overview

This PR improves lock error handling in the Swift PowerSync SDK by removing the need for custom TransactionCallback and LockCallback wrapper classes. The changes address Swift/Objective-C compatibility issues and compiler warnings related to optionality mismatches.

• Removes custom callback wrapper classes that had Swift 6 compatibility issues
• Replaces callback wrappers with new Kotlin SDK wrapper functions
• Introduces standardized error handling using PowerSyncResult enum

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
Sources/PowerSync/Kotlin/TransactionCallback.swift	Completely removes the file containing custom callback wrapper classes
Sources/PowerSync/Kotlin/KotlinPowerSyncDatabaseImpl.swift	Updates method calls to use new wrapper functions and adds helper functions for error handling

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[simolus3]

This looks good to me, I also like that this lets us remove Swift-specific logic from the :core Kotlin project.